I’m GMing a 1-on-1 campaign (it’s all homebrew, by the way). My player likes to weigh in on what’s happening, and sometimes oversteps her boundary into GMing territory. I let it slide a lot, since it doesn’t affect the plot much if at all and adds some character to the story.
In this particular game, she works for some agency and is tasked to infiltrate this grand palace in a foreign state and investigate the king because of some human rights violations. The problem is that it’s definitely a monarchy and it’s ruled by a long line of dragons (who can change to human form), and they kill anyone they wish.
When she infiltrated the temple, she worked her way up to being maid for the king. Through some investigation and kidnapping, she found out that the "king" is actually the king’s sister; the actual king is attending a college secretly because it is highly against tradition to go to higher education, so the sister is pretending to be her brother.
The people found this out via a god that is secretly pulling the strings of the whole operation, and they tried to kill the royal family, who escaped with my player's character. The PC recommended to them that the people probably hate them so much they should probably give up power and become a democratic state; her brother hates that idea, but my PC demands it.
When my PC didn’t get her way, she snapped him away to be a prisoner with her father, who the player apparently decided was a super powerful "Deus Ex Machina" character (she’s just a vampire, by the way). I talk to the player outside the game and let her know that she can’t really decide that, and we continue.
Since the people found out, they rioted; apparently my player decided, "Nope, that’s all gone in a week, and a democratic government forms, and it’s all happy flowers and sunshine." So I’m planning on her brother going full silver dragon (which it’s been established he can do) and just kill-switching everyone to show my PC who’s the GM.
I feel like my PC is trying to run the campaign and I’m considering just kill-switching everyone and her character. I’m a bad and new GM, so if anyone with experience can tell me how to deal with this better than just killing everyone, I’d like to know.